U.S. patent number 8,394,119 [Application Number 13/407,044] was granted by the patent office on 2013-03-12 for stents having radiopaque mesh.
This patent grant is currently assigned to Covidien LP. The grantee listed for this patent is Brian S. Carion, Richard S. Kusleika, Steven G. Zaver. Invention is credited to Brian S. Carion, Richard S. Kusleika, Steven G. Zaver.
United States Patent |
8,394,119 |
Zaver , et al. |
March 12, 2013 |
Stents having radiopaque mesh
Abstract
A stent including a mesh made of strands. The mesh has at least
one radiopaque strand and at least one non-radiopaque strand, and
the at least one radiopaque strand and the at least one
non-radiopaque strand each have different diameters. Each strand
has an index of wire stiffness EI, where EI is the mathematical
product of the Young's modulus (E) and the second moment of area
(I). The EI of all strands in the mesh is no more than five times
the EI of the strand having the smallest EI of any of the
strands.
Inventors: |
Zaver; Steven G. (Plymouth,
MN), Carion; Brian S. (White Bear Lake, MN), Kusleika;
Richard S. (Eden Prairie, MN) |
Applicant: |
Name |
City |
State |
Country |
Type |
Zaver; Steven G.
Carion; Brian S.
Kusleika; Richard S. |
Plymouth
White Bear Lake
Eden Prairie |
MN
MN
MN |
US
US
US |
|
|
Assignee: |
Covidien LP (Mansfield,
MA)
|
Family
ID: |
38229012 |
Appl.
No.: |
13/407,044 |
Filed: |
February 28, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120158124 A1 |
Jun 21, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11708651 |
Feb 20, 2007 |
8152833 |
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60775818 |
Feb 22, 2006 |
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Current U.S.
Class: |
606/200 |
Current CPC
Class: |
A61F
2/844 (20130101); A61F 2/0105 (20200501); A61F
2/90 (20130101); A61F 2/06 (20130101); A61F
2230/0067 (20130101); A61F 2002/018 (20130101); A61F
2250/0018 (20130101); A61F 2230/0006 (20130101); A61F
2002/016 (20130101); A61F 2250/0032 (20130101); A61F
2250/0098 (20130101); A61F 2310/00149 (20130101); A61F
2310/00071 (20130101); A61F 2310/00137 (20130101) |
Current International
Class: |
A61M
29/00 (20060101) |
Field of
Search: |
;606/108,194,200
;623/1.11-1.13,1.15,1.2,1.34 |
References Cited
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WO |
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WO-2009/105710 |
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Aug 2009 |
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WO |
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Other References
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Artery Aneurysm with Double Stent Placement: Case Report AJNR Am J
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applicant .
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Primary Examiner: Severson; Ryan
Assistant Examiner: Cronin; Ashley
Attorney, Agent or Firm: Kertz, Esq.; Mark J.
Parent Case Text
This application is a continuation of U.S. application Ser. No.
11/708,651, filed Feb. 20, 2007, which claims the benefit of U.S.
Provisional Application No. 60/775,818, filed Feb. 22, 2006,
entitled "Embolic Protection System Having Radiopaque Filter Mesh,"
the contents of each of which are hereby incorporated by reference
herein.
Claims
What is claimed is:
1. A stent comprising a mesh, the mesh comprising at least one
radiopaque strand and at least one non-radiopaque strand, the at
least one radiopaque strand and the at least one non-radiopaque
strand each having different cross-sectional dimensions, and
wherein each of the strands has an index of wire stiffness EI,
where EI is the mathematical product of the Young's modulus (E) and
the second moment of area (I), and wherein the EI of each of the
strands is no more than five times the EI of a strand having the
smallest EI of any of the strands.
2. The stent of claim 1, wherein the mesh is self-expanding.
3. The stent of claim 1, wherein the mesh is self-contracting.
4. The stent of claim 1, wherein the mesh is tubular.
5. The stent of claim 4, wherein the mesh is braided.
6. The stent of claim 1, wherein each strand has a round
cross-section.
7. The stent of claim 6, wherein the mesh comprises only two types
of strands, a first type being a radiopaque strand and having a
cross-sectional dimension D1 and a second type being a
non-radiopaque strand and having a cross-sectional dimension
D2.
8. The stent of claim 7, wherein both the first and second types of
strands are monofilaments.
9. The stent of claim 1, wherein the Young's modulus of the
radiopaque strand and the Young's modulus of the non-radiopaque
strand differ by 10 percent or more.
10. The stent of claim 1, wherein the Young's modulus of the
radiopaque strand and the Young's modulus of the non-radiopaque
strand differ by 20 percent or more.
11. The stent of claim 1, wherein the mesh comprises more
radiopaque strands than non-radiopaque strands.
12. The stent of claim 1, wherein the mesh comprises more
non-radiopaque strands than radiopaque strands.
13. The stent of claim 1, wherein the EI of each of the strands is
no more than four times the EI of a strand having the smallest EI
of any of the strands.
14. The stent of claim 1, wherein the EI of each of the strands is
no more than two times the EI of a strand having the smallest EI of
any of the strands.
15. The stent of claim 14, wherein the largest cross-sectional
dimension of a strand is no more than two times the smallest
cross-sectional dimension of any other strand.
16. The stent of claim 1, wherein the EI of each of the strands is
no more than 1.5 times the EI of a strand having the smallest EI of
any of the strands.
17. The stent of claim 1, wherein the EI of each of the strands is
no more than 1.3 times the EI of a strand having the smallest EI of
any of the strands.
18. The stent of claim 1, wherein the mesh comprises pores and when
the mesh is at rest in free space no pore has an area more than
five times the mesh pore size, the mesh pore size being the average
area of five pores serially adjacent to the pore.
19. The stent of claim 1, wherein the mesh comprises pores and when
the mesh is at rest in free space no pore has an area more than
four times the mesh pore size, the mesh pore size being the average
area of five pores serially adjacent to the pore.
20. The stent of claim 1, wherein the mesh comprises pores and when
the mesh is at rest in free space no pore has an area more than
three times the mesh pore size, the mesh pore size being the
average area of five pores serially adjacent to the pore.
21. The stent of claim 1, wherein the mesh comprises pores and when
the mesh is at rest in free space no pore has an area more than two
times the mesh pore size, the mesh pore size being the average area
of five pores serially adjacent to the pore.
22. The stent of claim 1, wherein the mesh comprises pores and when
the mesh is at rest in free space no pore has an area more than 1.5
times the mesh pore size, the mesh pore size being the average area
of five pores serially adjacent to the pore.
23. The stent of claim 1, wherein the mesh comprises pores and when
the mesh is at rest in free space no pore has an area more than 1.2
times the mesh pore size, the mesh pore size being the average area
of five pores serially adjacent to the pore.
24. The stent of claim 1, wherein the mesh comprises at least two
types of strands, each strand having a round cross-section, a first
type of strand being a radiopaque strand and having a
cross-sectional dimension D1 and a second type of strand being a
non-radiopaque strand and having a cross-sectional dimension D2,
cross-sectional dimension D1 being larger than cross-sectional
dimension D2, wherein the mesh comprises pores and when the mesh is
at rest in free space no pore adjacent to a strand having a
cross-sectional dimension D1 has an area more than five times the
mesh pore size, the mesh pore size being the average area of five
pores serially adjacent to the pore.
25. The stent of claim 1, wherein the mesh comprises at least two
types of strands, each strand having a round cross-section, a first
type of strand being a radiopaque strand and having a
cross-sectional dimension D1 and a second type of strand being a
non-radiopaque strand and having a cross-sectional dimension D2,
cross-sectional dimension D1 being larger than cross-sectional
dimension D2, wherein the mesh comprises pores and when the mesh is
at rest in free space no pore adjacent to a strand having a
cross-sectional dimension D1 has an area more than two times the
mesh pore size, the mesh pore size being the average area of five
pores serially adjacent to the pore.
26. The stent of claim 1, wherein the at least one radiopaque
strand is made of homogeneous metal or metal alloy.
27. The stent of claim 26, wherein the at least one radiopaque
strand is selected from the group consisting of strands made of
gold, platinum, tungsten, tantalum, and alloys thereof.
28. The stent of claim 1, wherein the at least one non-radiopaque
strand is made of metal.
29. The stent of claim 28, wherein the at least one non-radiopaque
strand is selected from the group consisting of strands made of
stainless steel and nitinol.
30. The stent of claim 28, wherein the at least one non-radiopaque
strand is superelastic.
31. The stent of claim 1, wherein the largest cross-sectional
dimension of a strand is no more than five times the smallest
cross-sectional dimension of any other strand.
32. The stent of claim 1, wherein the largest cross-sectional
dimension of a strand is no more than four times the smallest
cross-sectional dimension of any other strand.
33. The stent of claim 1, wherein the largest cross-sectional
dimension of a strand is no more than two times the smallest
cross-sectional dimension of any other strand.
34. The stent of claim 1, wherein the largest cross-sectional
dimension of a strand is no more than 1.5 times the smallest
cross-sectional dimension of any other strand.
35. The stent of claim 1, wherein the at least one radiopaque
strand is a monofilament.
36. The stent of claim 1, wherein the at least one non-radiopaque
strand is a monofilament.
37. The stent of claim 1, wherein the at least one radiopaque
strand is a multifilament wire.
38. The stent of claim 1, wherein at least one strand is a
monofilament wire from which some material has been removed in the
form of slots.
39. The stent of claim 1, wherein the at least one non-radiopaque
strand is made of nitinol.
40. The stent of claim 1, wherein the cross-sectional dimensions
are diameters.
41. The stent of claim 1, wherein the mesh is at least partially
occlusive to flow of fluid or particles therethrough.
42. A method of deploying a stent in a lumen defined by the walls
of a vessel in a patient's body comprising: providing the stent,
the stent comprising a mesh, the mesh comprising at least one
radiopaque strand and at least one non-radiopaque strand, the at
least one radiopaque strand and the at least one non-radiopaque
strand each having different cross-sectional dimensions, and
wherein each of the strands has an index of wire stiffness EI,
where EI is the mathematical product of the Young's modulus (E) and
the second moment of area (I), and wherein the EI of each of the
strands is no more than five times the EI of a strand having the
smallest EI of any of the strands; delivering the stent
percutaneously to a region of interest in the lumen of the
patient's body; and using fluoroscopy to visualize the stent in the
lumen of the patient's body.
43. The method of claim 42, wherein the mesh is self-expanding.
44. The method of claim 42, wherein the mesh is
self-contracting.
45. The method of claim 42, wherein the at least one radiopaque
strand is made of homogeneous metal or metal alloy.
46. The method of claim 42, whereby the mesh at least partially
occludes flow of fluid or particles therethrough.
Description
FIELD OF THE INVENTION
The present invention relates to embolic protection systems, and,
more particularly, to embolic protection systems for use in blood
vessels.
BACKGROUND OF THE INVENTION
Vessels are commonly treated to reduce or eliminate narrowings
caused by arteriosclerotic disease. Interventional treatments can
include use of balloon angioplasty, stenting, thrombectomy,
atherectomy, and other procedures. During treatment particulate
debris can be generated at the treatment site. Infarcts, strokes,
and other major or minor adverse events are caused when debris
embolizes into vasculature distal to the treatment site.
To prevent embolization of debris, embolic protection devices have
been developed. During a procedure such devices can be placed
distal or proximal to the treatment site. Embolic protection
devices can remove emboli from the bloodstream by filtering debris
from blood, by occluding blood flow followed by aspiration of
debris, or can cause blood flow reversal to effect removal of
debris. The shape, length and other characteristics of an embolic
protection device are typically chosen based on the anatomical
characteristics in the vicinity of the treatment site. However,
some anatomies present specific challenges due to the anatomical
shape or configuration.
Difficulties can arise where embolic protection devices are not
properly deployed within the anatomy. For example, if a device does
not properly engage a lumenal wall, leaving a gap, then particulate
matter entrained in a fluid in the lumen can bypass the protection
device. It would be an advantage to be able to visualize whether or
not there are gaps between the embolic protection device and the
lumenal wall. Also, when a protection device is being advanced or
withdrawn from a lumen it may engage with an obstruction. The
obstruction may be a stent that has been placed in a blood vessel,
an area of plaque build-up, lumen tortuosity, or other structure.
The operator of the embolic protection device may need to employ
different techniques to advance or withdraw the device depending on
the cause of engagement. Thus, it would be advantageous for the
operator to be able to visualize the exact location of the device
in the lumen.
Difficulties can also arise when recovering an embolic protection
device. One problem that can occur is that the embolic protection
device may require excessive force during recovery, for example
when drawing the device into a recovery catheter. The causes of
such excessive force can vary. For example the device could be
filled with embolic debris and thereby not fit into the lumen of a
recovery catheter, the device may be caught on a structure such as
a stent or a catheter tip, or other causes. It would be
advantageous to the operator to visualize the embolic protection
device so that appropriate actions can be taken so as to
successfully recover the device. Further discussion of these issues
is provided in U.S. Patent Publication No. 2002/0188314 A1, by
Anderson et. al., entitled "Radiopaque Distal Embolic Protection
Device", the contents of which are incorporated herein by
reference.
The current art employs a variety of approaches to solve the
problem of visualizing an embolic protection device in a patient.
All of the current approaches have limitations. For example, some
devices have radiopaque coatings; however coatings may become
separated from the underlying substrate. Radiopaque filler
materials have been employed in polymer film devices; however the
fillers detract from the mechanical properties of the films and the
filler/film composites, being thin, are not very visible. Strands
of drawn filled tubing (DFT) have been used and have good
mechanical and radiopacity characteristics; however DFT is
expensive. Individual strands of radiopaque wire, such as platinum,
gold, tungsten, and their alloys have good radiopacity but can have
unsuitable strength or elastic yield limits, and when comprising a
portion of the wires in a woven structure such as a braid, can
alter the braid wire spacing in the vicinity of the strand of
radiopaque wire due to differing mechanical properties compared to
neighboring non-radiopaque wires. For some filter devices, uniform
wire spacing is desired and altered braid wire spacing can cause
unacceptably large pores in the braid.
Accordingly, a need exists for an embolic protection device having
improved radiopacity that is inexpensive, durable, provides
visibility to the appropriate regions of the device, and which uses
technology that does not compromise the performance of the
device.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an embolic
protection device comprises a woven mesh comprising radiopaque and
non-radiopaque wires. The mechanical properties of the radiopaque
wires are selected to match the mechanical properties of the
non-radiopaque wires. The non-radiopaque wires can be superelastic.
The radiopaque wires are woven into pre-programmed locations so
that after processing the woven mesh into a device the radiopaque
wires will concentrate at a preferred location within the device. A
method is provided in which the device operator visualizes the
radiopaque wires so as to guide how the device is utilized in a
patient.
The invention provides a device for filtering emboli from blood
flowing through a lumen defined by the walls of a vessel in a
patient's body, comprising: a filter element being expandable from
a collapsed configuration when the filter element is restrained to
an expanded configuration when the filter element is unrestrained,
wherein the filter element comprises a mesh comprising strands,
each strand having a diameter, the mesh comprising at least one
radiopaque strand and at least one non-radiopaque strand, and
wherein each strand has an index of wire stiffness EI, where EI is
the mathematical product of the Young's modulus (E) and the second
moment of area (I), and wherein the largest EI of a strand is no
more than five times the smallest EI of a strand.
The invention provides a method of deploying a device for filtering
emboli from blood flowing through a lumen defined by the walls of a
vessel in a patient's body comprising: providing the device for
filtering emboli, the device comprising a filter element being
expandable from a collapsed configuration when the filter element
is restrained to an expanded configuration when the filter element
is unrestrained, wherein the filter element comprises a mesh
comprising strands, each strand having a diameter, the mesh
comprising at least one radiopaque strand and at least one
non-radiopaque strand, and wherein each strand has an index of wire
stiffness EI, where EI is the mathematical product of the Young's
modulus (E) and the second moment of area (I), and wherein the
largest EI of a strand is no more than five times the smallest EI
of a strand; delivering the device percutaneously to a region of
interest in the lumen of the patient's body; and using fluoroscopy
to visualize the filter element in the lumen of the patient's
body.
The invention provides a mesh comprising strands, each strand
having a diameter, the mesh comprising at least one radiopaque
strand and at least one non-radiopaque strand, and wherein each
strand has an index of wire stiffness EI, where EI is the
mathematical product of the Young's modulus (E) and the second
moment of area (I), and wherein the largest EI of a strand is no
more than five times the smallest EI of a strand.
It is to be understood that both the foregoing general description
and the following detailed description are exemplary and
explanatory and are intended to provide further explanation of the
invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and further advantages of the invention may be better
understood by referring to the following description in conjunction
with the accompanying drawings.
FIGS. 1A to 1C illustrate conceptually a partial plan view of
braided tubular mesh having radiopaque and non-radiopaque wires in
accordance with the present invention.
FIG. 2 illustrates conceptually a side view of a filter formed from
braided tubular mesh in accordance with the present invention.
FIG. 3 illustrates conceptually a method for forming a filter from
braided tubular mesh in accordance with the present invention.
FIGS. 4A and 4B illustrate conceptually plan views of braided mesh
in accordance with the present invention.
FIGS. 5A to 5E illustrate cross sectional or side views of wires in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides a device for filtering emboli from blood
flowing through a lumen defined by the walls of a vessel in a
patient's body, comprising: a filter element being expandable from
a collapsed configuration when the filter element is restrained to
an expanded configuration when the filter element is unrestrained,
wherein the filter element comprises a mesh comprising strands,
each strand having a diameter, the mesh comprising at least one
radiopaque strand and at least one non-radiopaque strand, and
wherein each strand has an index of wire stiffness EI, where EI is
the mathematical product of the Young's modulus (E) and the second
moment of area (I), and wherein the largest EI of a strand is no
more than five times the smallest EI of a strand.
In one embodiment, the device further comprises an elongate support
member and the filter element is carried on a portion of the
elongate support member. In another embodiment, the filter element
has proximal and distal portions and a central portion, the filter
element having a shape in the expanded configuration which defines
a cavity having a proximal facing opening. In one embodiment, the
filter element has a proximal facing opening portion and this
portion is radiopaque.
The filter element may be self-expanding or self-contracting. The
mesh may be tubular and/or braided. In one embodiment, each strand
has a round cross-section. In another embodiment, the mesh
comprises only two types of strands, a first type being a
radiopaque strand and having a diameter D1 and a second type being
a non-radiopaque strand and having a diameter D2. In one
embodiment, the Young's modulus of the radiopaque strand and the
Young's modulus of the non-radiopaque strand differ by 10 percent
or more. In another embodiment, the Young's modulus of the
radiopaque strand and the Young's modulus of the non-radiopaque
strand differ by 20 percent or more.
In one embodiment, the mesh comprises more radiopaque strands than
non-radiopaque strands. In another embodiment, the mesh comprises
more non-radiopaque strands than radiopaque strands. In embodiments
of the invention, the largest EI of a strand is no more than four
times the smallest EI of a strand, the largest EI of a strand is no
more than two times the smallest EI of a strand, the largest EI of
a strand is no more than 1.5 times the smallest EI of a strand, or
the largest EI of a strand is no more than 1.3 times the smallest
EI of a strand.
In embodiments of the invention, the mesh comprises pores and when
the mesh is at rest in free space no pore has an area more than
five times the mesh pore size, when the mesh is at rest in free
space no pore has an area more than four times the mesh pore size,
when the mesh is at rest in free space no pore has an area more
than three times the mesh pore size, when the mesh is at rest in
free space no pore has an area more than two times the mesh pore
size, when the mesh is at rest in free space no pore has an area
more than 1.5 times the mesh pore size, or when the mesh is at rest
in free space no pore has an area more than 1.2 times the mesh pore
size. The mesh pore size is the average area of five pores serially
adjacent to the pore.
In embodiments of the invention, the mesh comprises at least two
types of strands, each strand having a round cross-section, a first
type of strand being a radiopaque strand and having a diameter D1
and a second type of strand being a non-radiopaque strand and
having a diameter D2, diameter D1 being larger than diameter D2,
wherein the mesh comprises pores and when the mesh is at rest in
free space no pore adjacent to a strand having a diameter D1 has an
area more than five times the mesh pore size, the mesh pore size
being the average area of five pores serially adjacent to the pore.
In other related embodiments, when the mesh is at rest in free
space no pore adjacent to a strand having a diameter D1 has an area
more than four times the mesh pore size, more than three times the
mesh pore size, more than two times the mesh pore size, more than
1.5 times the mesh pore size, or more than 1.2 times the mesh pore
size.
In one embodiment, the at least one radiopaque strand is made of
homogeneous metal or metal alloy. In another embodiment, the at
least one radiopaque strand is selected from the group consisting
of strands made of gold, platinum, tungsten, tantalum, and alloys
thereof. Other radiopaque substances may be used. In an embodiment,
the at least one non-radiopaque strand is made of metal. In one
embodiment, the at least one non-radiopaque strand is selected from
the group consisting of strands made of stainless steel and
nitinol. Other non-radiopaque substances may be used. In one
embodiment, the at least one non-radiopaque strand is
superelastic.
In embodiments of the invention, the largest diameter of a strand
is no more than five times the smallest diameter of a strand, the
largest diameter of a strand is no more than four times the
smallest diameter of a strand, the largest diameter of a strand is
no more than two times the smallest diameter of a strand, or the
largest diameter of a strand is no more than 1.5 times the smallest
diameter of a strand. In one embodiment, the largest diameter of a
strand is no more than two times the smallest diameter of a strand,
and the largest EI of a strand is no more than two times the
smallest EI of a strand.
In one embodiment, the at least one radiopaque strand is a
monofilament. In one embodiment, the at least one non-radiopaque
strand is a monofilament. In another embodiment, the mesh comprises
only two types of strands, a first type being a radiopaque strand
and having a diameter D1 and a second type being a non-radiopaque
strand and having a diameter D2, and both the first and second
types of strands are monofilaments. In one embodiment, the at least
one radiopaque strand is a multifilament wire. In another
embodiment, at least one strand is a monofilament wire from which
some material has been removed in the form of slots. In one
embodiment, the at least one non-radiopaque strand is made of
nitinol.
The invention provides a method of deploying a device for filtering
emboli from blood flowing through a lumen defined by the walls of a
vessel in a patient's body comprising: providing the device for
filtering emboli, the device comprising a filter element being
expandable from a collapsed configuration when the filter element
is restrained to an expanded configuration when the filter element
is unrestrained, wherein the filter element comprises a mesh
comprising strands, each strand having a diameter, the mesh
comprising at least one radiopaque strand and at least one
non-radiopaque strand, and wherein each strand has an index of wire
stiffness EI, where EI is the mathematical product of the Young's
modulus (E) and the second moment of area (I), and wherein the
largest EI of a strand is no more than five times the smallest EI
of a strand; delivering the device percutaneously to a region of
interest in the lumen of the patient's body; and using fluoroscopy
to visualize the filter element in the lumen of the patient's body.
The device used in this method can be any of the embodiments
described herein. In one embodiment, the filter element has
proximal and distal portions and a central portion, the filter
element having a shape in the expanded configuration which defines
a cavity having a proximal facing opening, the filter element has a
proximal facing opening portion and this portion is radiopaque, and
the proximal facing opening portion of the filter element is
visualized to confirm that this portion is adequately deployed
against the walls of the vessel.
The invention provides a mesh comprising strands, each strand
having a diameter, the mesh comprising at least one radiopaque
strand and at least one non-radiopaque strand, and wherein each
strand has an index of wire stiffness EI, where EI is the
mathematical product of the Young's modulus (E) and the second
moment of area (I), and wherein the largest EI of a strand is no
more than five times the smallest EI of a strand. The mesh can be
any of the embodiments described herein in connection with the mesh
that is part of the device for filtering emboli.
In the discussion below the invention is described using as
examples filters comprised of braided metal strands. It is to be
understood that the invention is not limited to the examples below.
For example, the mesh of the invention can be comprised of strands
that are woven, non-woven, or knitted to form the mesh. The mesh
can have uniform strand spacing so as to define a structure with
relatively uniformly sized openings between strands or can have
variable strand spacing so as to define a structure with varied
size openings between strands. The mesh can be coated with an
elastic polymer film in whole or in part, or with another material,
so as to reduce in size or eliminate the openings between strands.
The coated mesh may be partially or totally occlusive to flow of
fluid or particles therethrough. In some embodiments the metal
strands may be superelastic alloys comprised of radiopaque alloy
constituents. In some preferred embodiments a metal strand is
comprised of nickel-titanium-platinum or nickel-titanium-tantalum
alloy. In addition, some or all of the strands may be comprised of
materials other than metal including but not limited to engineering
polymers such as PEEK (polyetheretherketone), liquid crystal,
polyamide, or polyester; ceramics; glass-ceramics; metallic
glasses; or other materials known in the art. In some embodiments
the aforementioned materials can be comprised of radiopaque filler
materials. In some embodiments the strands are homogeneous in the
sense that they are not comprised of separate layers. It is further
understood that the cross section of some or all of the strands can
be round, ovoid, square, rectangular, triangular, irregular,
symmetrical, non-symmetrical, or other shapes.
FIGS. 1A to 1C illustrate conceptually partial plan views of
braided meshes having radiopaque and non-radiopaque wires in
accordance with the present invention. For clarity only the braided
wires along half of the braided perimeter of the tube are shown.
Braided wires arranged below the illustrated wires are not shown.
Also for clarity the radiopaque wires in FIGS. 1A to 1C are shown
as having slightly increased diameter as compared to non-radiopaque
wires, although it is understood that the relative sizes of the
radiopaque and non-radiopaque filaments may not be as illustrated
and generally will be determined according to the teachings below.
Further, strands are generally illustrated as intersecting at
angles of approximately 90.degree., although it is understood that
within the scope of the invention strands can intersect or overlap
at any angle.
In FIG. 1A braided tubular mesh 10 is comprised of interwoven wires
12 and 14. Non-radiopaque wires 12 comprise the majority of the
wires and two sets of adjacent pairs of radiopaque wires 14 are
interwoven with the non-radiopaque wires 12. Braided tubular mesh
10 has a number of pores 16 defined by the wires, and each pore has
a size, the pore size defined as the area bounded by the wires
forming the perimeter of the pore. Braided tubular mesh 10 can be
formed of a variety of materials. Metal wires are preferred, and
superelastic nitinol is particularly preferred for the
non-radiopaque wires 12. Braided tubular mesh 10 has a diameter D,
which is the diameter of the braided tubular mesh at rest in free
space. Diameter D is determined by braiding processing parameters
and wire diameters used. Heat treatments may be used to help
stabilize diameter D, especially when wire materials such as
nitinol are used. A braid comprised of nitinol wire is typically
heat set at 400 to 600.degree. C. for 1 to 60 minutes to stabilize
the braid diameter. In a preferred embodiment nitinol wire is heat
set at 425.degree. C. for 20 minutes to stabilize the braid
diameter. Non-nitinol wires may be annealed at temperatures that
will stress relieve or even recrystallize the materials in order to
stabilize the tubular braid diameter. It is understood that
self-expanding or self-contracting devices can be comprised of
braided tubular mesh 10. Self-expanding devices are devices in
which, during use, braided tubular mesh 10 is compressed and
subsequently allowed to expand without application of forces
external to the mesh for causing expansion. Self-contracting
devices are devices in which, during use, braided tubular mesh 10
is expanded and subsequently allowed to contract without
application of forces external to the mesh for causing contraction.
It is advantageous to construct self-expanding or self-contracting
devices at least in part from wires that have elastic strain limits
higher than the elastic strains generated in the wires during use
of these devices, and to process the wires so as to retain or
enhance the elastic strain limits of the wires chosen. Devices
which are neither self-expanding nor self-contracting may also be
comprised of braided tubular mesh 10. Devices of the invention may
also be comprised of braided tubular mesh or strands which deform
upon expansion or contraction. The strands of such devices may be
processed or chosen such that the elastic strain limit of the
strands are less than the elastic strains generated in the strand
during use of the device.
FIG. 1B illustrates braided tubular mesh 10 comprised of a single
radiopaque wire 14 interwoven with non-radiopaque wires 12 and FIG.
1C illustrates braided tubular mesh 10 comprised primarily of
radiopaque wires 14 interwoven with a minority of non-radiopaque
wires 12. It is understood that multiple combinations of interwoven
radiopaque and non-radiopaque wires 14 and 12 are possible within
the scope of the invention, and that the number, proportion, and
positioning of radiopaque and non-radiopaque wires within the mesh
will be chosen based on the desired device functional and other
requirements.
FIG. 2 illustrates conceptually a side view of filter 20 formed
from a braided tubular mesh 10 comprised of interwoven radiopaque
and non-radiopaque wires 12 and 14 in accordance with the present
invention. For clarity the wires on the back side of the filter are
not shown. Filters similar to that shown in FIG. 2 can be made by
enlarging a pore in the side wall of the braid using a tapered
mandrel and stabilized in the desired shape by heat treating on a
mandrel. Processing details for making a filter using these methods
are disclosed in U.S. Pat. No. 6,325,815 B1 to Kusleika et al.,
entitled "Temporary Vascular Filter", the contents of which are
incorporated herein by reference. In filter 20, radiopaque wires 14
are bunched at the opening of the filter, providing improved
visibility under fluoroscopy of the perimeter 26 of mouth 24 of the
filter. In an alternate embodiment radiopaque wires 14 are bunched
distal to mouth 24 of the filter, providing improved visibility
under fluoroscopy of the portion of the filter apposing a vessel
wall during use. Radiopaque wires 14 also extend throughout the
body 22 of the filter mesh, providing visibility under fluoroscopy
to the body of the filter.
FIG. 3 illustrates conceptually a method for forming filter 20 from
braided tubular mesh 10 comprised of interwoven radiopaque and
non-radiopaque wires 12 and 14 in accordance with the present
invention. Pore 35 is chosen as the pore to enlarge into mouth 24
of filter 20. Pore 35 is chosen specifically such that radiopaque
wires 14a will be bunched along the perimeter 26 of filter mouth 24
during the filter forming process. In FIG. 3, pore 35 is located 3
pores from the intersecting pore 38 of radiopaque filaments 14a. In
one example, braided tubular mesh 10 is comprised of 36 wires and
has a diameter D of 3 mm before forming into filter 20. Two pairs
of radiopaque wires 14a are interwoven into tubular mesh 10 as
illustrated in FIG. 3, and the remaining 32 wires are
non-radiopaque nitinol. Pore 35 is located 8 pores from
intersecting pore 38 of radiopaque filaments 14a. In another
example, braided tubular mesh 10 is comprised of 72 wires and has a
diameter D of 7 mm before forming into filter 20. Two pairs of
radiopaque wires 14a are interwoven into tubular mesh 10 as
illustrated in FIG. 3, and the remaining 68 wires are
non-radiopaque. Pore 35 is located 15 pores from intersecting pore
38 of radiopaque filaments 14a. It is understood that the location
chosen for piercing braided tubular mesh 10 comprised of interwoven
radiopaque and non-radiopaque wires 12 and 14 will vary within the
scope of the invention and will depend on the application
contemplated and results desired.
When adding radiopaque wires to a mesh comprised primarily of
non-radiopaque wires it is often desired to increase the diameter
of the radiopaque wire relative to the diameter of the
non-radiopaque wire so as to increase the visibility of the
radiopaque wire under fluoroscopy. FIG. 4A illustrates the effect
of adding a larger wire 42 to a mesh 40, wherein the pore sizes 45
adjacent to the larger wires are increased in area as compared to
pore sizes 47 in the portion of the mesh comprised of smaller wires
44 due to the presence of the larger wire 42 relative to the
adjacent smaller wires 44 in the mesh. For certain applications,
including some filter devices, large pores in the braid can be
unacceptable because the large pores will allow large emboli to
pass through the filter.
FIG. 4B illustrates braided tubular mesh 40 comprised of a large
wire 42 and multiple smaller wires 44 having uniformly sized pores
48, a configuration preferred for filtering applications such as
for distal embolic protection devices. The uniformly sized pores
illustrated in FIG. 4B are achieved by using similar stiffness
wires in the mesh. A useful index of wire stiffness is EI, where E
is the Young's modulus of the wire material, I is the second moment
of area of the wire, and EI is the mathematical product of the two.
In a preferred embodiment of the device, the largest EI of wires
used in the device is no more than 5 times the smallest EI of wires
used in the device. In a more preferred embodiment of the device,
the largest EI of wires used in the device is no more than 4 times
the smallest EI of wires used in the device. In a further preferred
embodiment of the device, the largest EI of wires used in the
device is no more than 2 times the smallest EI of wires used in the
device. In a further preferred embodiment of the device, the
largest EI of wires used in the device is no more than 1.5 times
the smallest EI of wires used in the device. In a further preferred
embodiment of the device, the largest EI of wires used in the
device is no more than 1.3 times the smallest EI of wires used in
the device.
Referring again to FIG. 4A, the area of pore 45a adjacent to large
wire 42 is much greater than the average area of the five pores
47a, 47b, 47c, 47d, and 47e serially adjacent to pore 45a. For
convenience we hereby define the average area of the five pores
47a, 47b, 47c, 47d, and 47e serially adjacent to pore 45a as the
mesh pore size. This definition allows us to apply the inventive
teachings herein to various filter shapes with varying pore sizes,
including tapered filters where the pore size varies along the
length of the filter, such as the filter illustrated in FIG. 2. In
a preferred embodiment of the mesh at rest in free space, the size
of pore 45a adjacent to large wire 42 is no more than 5 times
larger than the mesh pore size. In a more preferred embodiment of
the mesh, the size of pore 45a adjacent to large wire 42 in the
mesh at rest in free space is no more than 4 times larger than the
mesh pore size. In a further preferred embodiment of the mesh, the
size of pore 45a adjacent to large wire 42 in the mesh at rest in
free space is no more than 3 times larger than the mesh pore size.
In a further preferred embodiment of the mesh, the size of pore 45a
adjacent to large wire 42 in the mesh at rest in free space is no
more than 2 times larger than the mesh pore size. In a further
preferred embodiment of the mesh, the size of pore 45a adjacent to
large wire 42 in the mesh at rest in free space is no more than 1.5
times larger than the mesh pore size. In a further preferred
embodiment of the mesh, the size of pore 45a adjacent to large wire
42 in the mesh at rest in free space is no more than 1.2 times
larger than the mesh pore size.
To achieve the uniform pore size illustrated in FIG. 4B various
approaches can be used to match wire stiffnesses. In one embodiment
a tubular braided mesh of monofilament 52 (see FIG. 5A) stainless
steel wires incorporates an interwoven monofilament wire having a
larger diameter than the stainless steel wires with the Young's
modulus of the interwoven larger wire less than that of stainless
steel. Suitable choices of material for the larger wire include
gold and platinum (see Table 1 below). The lower modulus of gold
and platinum relative to stainless steel will offset the larger
diameter of the radiopaque wire such that the calculated EI's of
the radiopaque and non-radiopaque wires will be equal or
similar.
TABLE-US-00001 TABLE 1 Material Young's Modulus, E (GPa) Gold 78
Nitinol (Austenitic) 75-83 Platinum 168 Tungsten 411 Tantalum 186
Stainless Steel 199
In an alternate embodiment, multifilament wires 53 can be used (see
FIG. 5B). The diameter of each individual filament 54 of a
multifilament wire is smaller than the overall diameter of the wire
53 and this allows higher modulus materials to be incorporated into
some or all of the filaments 54 of a larger multifilament wire 53.
For example, braided tubular mesh comprised of nitinol monofilament
wires could incorporate one or more interwoven multifilament wires
comprised of gold, platinum, tungsten, tantalum, or other
radiopaque materials. In one embodiment of a multifilament wire
more than one filament is twisted into a helical shape around a
central filament. In another embodiment of multifilament wire 53
individual monofilaments are interwoven into the braid adjacent to
each other as shown in FIG. 5E. It is understood that many other
combinations of filaments can be devised by one skilled in the art
within the scope of the invention.
In a further embodiment, FIGS. 5C and 5D illustrate slotted wire 56
in which monofilament wire 57 has had material removed in the form
of slots 58, for example by grinding. Slots 58 have opposing faces
59 and due to material having been removed from the perimeter of
the wire to form slots 58 the overall modulus of wire 56 is
reduced.
One example of deriving uniform pore size by matching wire
stiffnesses is as follows. Tubular braided mesh is comprised of 36
Nitinol monofilament wires of 0.003'' (0.0076 cm) diameter. It is
desired to improve the visibility of the mesh by substituting a
monofilament circular cross section tungsten wire for one of the
nitinol wires, and to do so without significantly changing the pore
size of the mesh. The appropriate diameter of the tungsten wire is
calculated as shown below. 1/.rho.=M/(E.times.I) Where .rho.=the
density of the material in bending, M=the bending moment, and E
& I are as defined above. Equating the bending moments of
nitinol and tungsten wires yields:
(E.sub.w.times.I.sub.w)/.rho..sub.w=M=(E.sub.NiTi.times.I.sub.NiTi).rho..-
sub.NiTi and I=(.pi.d.sup.2L.sup.3.rho.)/(48 g) Where .pi.=3.14159,
d=monofilament diameter, L=the unsupported transverse length of the
filament, and g=the gravitational constant
By combining terms:
E.sub.w.times.(.pi.d.sub.w.sup.2L.sub.w.sup.3.rho..sub.w)/(48
g.rho..sub.w)=E.sub.NiTi.times.(.pi.d.sub.NiTi.sup.2L.sub.NiTi.sup.3.rho.-
.sub.NiTi)/(48 g.rho..sub.NiTi) and by eliminating like terms:
E.sub.w.times.d.sub.w.sup.2=E.sub.NiTi.times.d.sub.NiTi.sup.2
Substituting known values and solving for d.sub.w yields
d.sub.w=0.0013''(0.0033 cm)
In another example, the appropriate diameter of gold wire to be
substituted into the mesh, using the same calculation as above
except substituting into the equations the material parameters of
gold in place of the parameters of tungsten, would be
d.sub.Au=0.0031'' (0.0079 cm).
In yet another example, the appropriate diameter of nitinol
monofilament wires to be braided with 0.0024'' (0.0061 cm) outer
diameter 1.times.7 stranded tungsten wire (constructed from a
central monofilament of tungsten surrounded by a ring of 6 tungsten
monofilaments of the same diameter as the central filament) into
tubular braided mesh having uniform pore size is calculated as
follows. The equations above are used to calculate EI for each
individual tungsten filament (having a filament diameter of
0.0008'' (0.002 cm) in this example). The EI of the stranded wire
is approximated as seven times that of one tungsten monofilament
(assuming the friction between filaments is small compared to the
bending stiffness of the filaments, therefore no adjustment is made
for friction). The equations above are solved for d.sub.NiTi by
equating EI for the nitinol wire with the calculated EI for the
tungsten stranded wire. In this example d.sub.NiTi is approximately
equal to 0.0047'' (0.012 cm). It is understood that improved
calculations for the stiffness of multifilament wire can be
employed as part of these calculations. Improved calculations may
account for frictional forces between strands, non-linear
configuration of some or all of the strands, or other factors.
Another means for achieving uniform pore size braided mesh
comprised of some radiopaque wires is by matching radiopaque and
non-radiopaque wire diameters. The smaller the distance between
interwoven radiopaque and non-radiopaque wires the greater the
variation in pore size caused by differing wire diameters. In a
preferred embodiment of the device, the largest diameter of wires
used in the device is no more than 5 times the smallest diameter of
wires used in the device. In a more preferred embodiment of the
device, the largest diameter of wires used in the device is no more
than 4 times the smallest diameter of wires used in the device. In
a further preferred embodiment of the device, the largest diameter
of wires used in the device is no more than 2 times the smallest
diameter of wires used in the device. In a further preferred
embodiment of the device, the largest diameter of wires used in the
device is no more than 1.5 times the smallest diameter of wires
used in the device. In a most preferred embodiment both the wire
diameter and the wire stiffness of both the radiopaque and
non-radiopaque wires are similar.
A method of using a device made from the inventive mesh is as
follows. An embolic protection device, made using methods similar
to those discussed in connection with FIG. 2, is delivered
percutaneously to a region of interest in the body of a patient
using methods known in the art. Optionally a catheter is used to
deliver the filter to the region of interest. Fluoroscopy is used
by the operator to visualize the mouth and the body of the filter
to ascertain that the filter is positioned appropriately in
relation to a treatment or diagnostic site, for example, positioned
such that the mouth of the filter is distal to a stenosis in an
artery, and also by example, positioned such that the body of the
filter is in a healthy region of vessel suitable for use as a
landing zone for the filter. The filter is then deployed and the
catheter (if used) is removed from the vicinity of the filter. The
operator uses fluoroscopy to ascertain that the mouth of the filter
is adequately deployed against the vessel wall with no gaps, distal
to the lesion, and proximal to any important side branch vessels.
Radiopaque contrast media may be injected at this time or at any
time to assist with visualization of the patient's anatomy. The
treatment site is treated, for example by dilating a lesion with a
balloon dilatation catheter and by deploying a stent or drug
eluting stent at the treatment site, although other methods known
in the art can be used.
After or during treatment or both, the operator may visualize the
mouth and body of the device and may adjust the position of the
device to assure, for example, that the device is properly located
along the length of the vessel and properly opposed to the vessel
wall. After treatment the device is recovered. Optionally a
catheter is used during the recovery process. At least a portion of
the filter is drawn into the recovery catheter (if used) and the
mouth and body of the filter are observed under fluoroscopy to
ascertain when the device is sufficiently drawn into the catheter.
If difficulty is encountered while drawing the filter into the
catheter the devices are again imaged under fluoroscopy and the
cause of the difficulty is diagnosed in part by observing the
radiopaque portions of the device. The filter (and recovery
catheter if used) are then withdrawn from the vessel. If resistance
to withdrawal is encountered then the devices are imaged under
fluoroscopy and the cause of resistance is determined and
eliminated.
While this document has described an invention mainly in relation
to braided tubular mesh used for embolic protection filtering
devices used in arteries, it is envisioned that the invention can
be applied to other conduits in the body as well including veins,
bronchi, ducts, ureters, urethra, and other lumens intended for the
passage of air, fluids, or solids. The invention can be applied to
other devices such as vena cava filters, stents, septal defect
closure devices, and other devices comprised of mesh having the
benefits described above.
While the various embodiments of the present invention have related
to embolic protection filtering devices, the scope of the present
invention is not so limited. Further, while choices for materials
and configurations have been described above with respect to
certain embodiments, one of ordinary skill in the art will
understand that the materials described and configurations are
applicable across the embodiments.
The above description and the drawings are provided for the purpose
of describing embodiments of the invention and are not intended to
limit the scope of the invention in any way. It will be apparent to
those skilled in the art that various modifications and variations
can be made without departing from the spirit or scope of the
invention. Thus, it is intended that the present invention cover
the modifications and variations of this invention provided they
come within the scope of the appended claims and their
equivalents.
* * * * *